This invention relates to a pipe bending device which is composed of a drive wheel, a plurality of guide wheels, a pair of guide molds and a mandrel. The guide mold includes a first guide mold and a second guide mold which are engaged respectively with the drive wheel and the guide wheels, the first guide mold being formed into a curve shape, the mandrel being inserted into the inner hole of the pipe, the end of the pipe being fixed at the end of the first guide mold. Hence the pipe can be stretched and bended by the first guide mold to form a curve the same with the curve of the first guide mold.
The conventional pipe bending device is shown in FIG. 1. The roller (R1) can be adjusted upwardly or downwardly and rotated around the shaft (C1), the roller (R2) and the roller (R3) being installed below the roller (R1) and rotated respectively around the shaft (C2) and the shaft (C3), furthermore the roller (R2) and the roller (R3) being installed at the same level (L). The pipe (4) is located between the roller (R1) and the rollers (R2) (R3). The pressure on the pipe (4) can be adjusted by the roller (R1). As the pipe goes through the roller (R1) and the rollers (R2) (R3), it is bended into a curve shape. The bending curvature of pipe is decided by the vertical distance between the roller (R1) and the rollers (R2) (R3), more longer of the vertical distance, more larger of the bending curvature, i.e. the bending curvature of the pipe being controlled by the operator to adjust the vertical distance between the roller (R1) and the rollers (R2,R3). It is very difficult for an operator to get an accurate bending curvature under such a condition. In addition the inner surface of the bending part may be deformed or can't be kept smooth.
The rollers (R2) (R3) produce an upward reaction force(F) on the pipe as the pipe goes through between the roller (R1) and the rollers (R2) (R3) so that the pipe can be bended upwardly at its two ends. Hence the end of the pipe has a large deflection and may cause a curling at its end.
The FIG. 1A shows another conventional pipe bending device, the end of pipe being fixed at the circumference of a drive wheel (W), the drive wheel (W) being rotated around a shaft (W1) to bend the pipe, according to such a kind of pipe bending method, the curvature radius (S) of the pipe must be the same with the curvature radius (r) of the drive wheel (W). If the curvature radius of pipe is very large, the drive wheel (W) must be manufactured into large dimension that may cause a larger manufacturing cost. Furthermore, it is very inconvenient for an operator to install or carry the large drive wheel.